1. Field of the Invention
The present invention relates to a technique for generating image data used in an inkjet printer and a technique for printing with a head for ejecting fine droplets of ink onto a printing medium.
2. Description of the Background Art
Conventionally used has been an inkjet printer provided with a head having a plurality of outlets (nozzles), where the head moves relatively to a printing paper and printing is performed by controlling ON/OFF of ejection of fine droplet of ink from each outlet. In such a printer, recently, ejected fine droplets are further downsized and outlets are arranged at higher density, in order to print a high-definition image.
It is confirmed unevenness (mura) appears in a printed image in the case that ejection operation of ink is continuously performed by a predetermined number or more of continuous outlets in a head, and it has been known such unevenness is caused by adjacent outlets which affect one another in ejecting ink (so-called cross talk). Unevenness by the cross talk between the outlets more remarkably appears with higher density of arrangement of the outlets (i.e., as an arrangement pitch of the outlets is made smaller).
Japanese Patent Application Laid-Open No. 2002-120366 (Document 1) discloses a technique for suppressing variations in ejection velocities of ink depending on cross talk between outlets by dividing nozzles included in a nozzle row into a plurality of groups and setting different driving voltages in respective groups. Japanese Patent Application Laid-Open No. 2006-27036 (Document 2) discloses a technique for suppressing variations in droplet velocities by cross talk between outlets, by treating a pulse width, where a velocity change rate becomes smaller in a relationship between the droplet velocity and the pulse width of a driving voltage waveform, as a pulse width of the driving voltage waveform which is actually used. It is described in Document 2 that causes of occurrence of the cross talk are vibration of constituent members in driving the nozzles, variation in pressure generated in ink pressure chambers of the driving nozzles, variation in driving voltage depending on the number of driving nozzles, or the like.
In the technique of Document 1, however, a plurality of waveform generating circuits for generating a plurality of kinds of driving waveforms, a circuit for selecting one of the plurality of kinds of driving waveforms for each nozzle and the like are required, so a construction of an apparatus is complicated and upsized to increase the manufacturing cost of the apparatus. In the technique of Document 2, a complicate operation for acquiring the relationship between the droplet velocity and the pulse width of the driving voltage waveform is required.